1. Field of the Invention
The present invention generally relates to a vertical semiconductor device package having a printed circuit board and heat spreader, and a module containing the packages. More particularly, the invention relates to a vertical semiconductor device package having a heat spreader which is directly attached to a semiconductor chip or the printed circuit board which comprises multiple metal layers, and a module having a plurality of the packages and a heat sink.
2. Description of the Related Arts
In the field of electronics, as power consumption increases due to higher speed transmission and processing of data, the amount of heat generation from the semiconductor increases. Accordingly, poor heat dissipation capability of a semiconductor package can adversely affect the reliability and the lifetime of the electronic device. For example, a junction temperature increase of approximately 10.degree. C. can reduce the lifetime of the device by about 50%. Therefore, in case of the high power package, the importance of the heat dissipation capability of the package has become greater than ever. Particularly, in memory devices such as DRAMs and SRAMs requiring fast data transmission speed, as well as in non-memory devices such as logic chips and power transistors, effective heat dissipation is an important issue.
The data processing speed of a memory chip being slower than that of the CPU (central processing unit) creates a bottleneck for data transmission. In DRAMs, data storage capacity has greatly increased generation after generation, but their speed to input and output the data has not improved enough to match that of the CPUs.
Recently, Rambus DRAM, which enhances the data transmission speed by removing the data bottleneck created by conventional DRAM, was developed and introduced by Rambus Inc. in the U.S. Rambus DRAMs may achieve high performance and high speed for synchronous imaging and three dimensional graphics by providing high speed data processing capability.
It is known that Rambus DRAM adopts a "bus type technique", in which the complicated data transmitting networks are simplified by arranging them in parallel.
Since I/O pads of the Rambus DRAM chip are aligned on the active front side of the chip along one edge, the corresponding leads or the corresponding pins of the package naturally protrude from only one edge of the package. Accordingly, Rambus DRAMs are packaged in two types of packages: SVPs (Surface Vertical Packages) and SHPs (Surface Horizontal Packages).
In an SVP, the leads protrude from one edge of the package and are perpendicularly bent outward, and the package is vertically mounted on a motherboard so that the bent portions of the leads are attached to the motherboard. However, the mounting area of an SVP on the motherboard is very small, for example, 1/7 of the mounting area of a conventional surface mount type package such as an SOJ (Small Outline J-lead Package), or 1/3 of the mounting area of a ZIP (Zigzag Inline Package). For secure mounting of the SVP on the motherboard, the unbent pins from both ends of the package are inserted in the holes in the motherboard, and dummy pins formed on both ends of the package are alternately bent in opposite directions to support the package.
The SHP has a similar structure to that of a TSOP (Thin Small Outline Package) and is mounted on the motherboard by functional pins, which are formed along one edge, and dummy pins, which are formed along the opposite edge for mounting the package. The mounting height of an SVP on the motherboard is greater than that of a SHP.
Although a 16-Mbit or a 18-Mbit Rambus DRAM can be packaged with leadframes as described above, 64 Mbit or larger Rambus DRAMs, which have greater electrical demands, are packaged on printed circuit boards which have multiple circuit layers. At this time, the maximum operational electric power of the Rambus DRAM is approximately 2.0.about.2.1 W, which may cause heat dissipation problem.
FIG. 1 and FIG. 2 show a conventional vertical semiconductor device package using a PCB (printed circuit board) 16. Referring to FIG. 1 and FIG. 2, a semiconductor chip 12 is attached to a front side of the PCB 16, on which copper wirings 22 are formed, by interposing a thermally conductive and electrically dielectric adhesive 24. Chip pads 14, which are formed on a front side of the chip 12, are connected to respective board pads 18 of the PCB 16 by metal wires 26 for the electrical connection with external circuitry. The board pads 18 are connected to respective connection pads 20, which are formed on one edge of the PCB 16, via the copper wirings 22, and the connection pads 20 of the PCB 16 are inserted into a slot on a motherboard 40. The chip 12 is encapsulated with a molding compound 28 to protect chip 12 from external environmental stress. A heat spreader 30 is attached to the back side of the PCB 16.
The heat dissipation route of the vertical semiconductor device package 10 is as follows. Heat generated from the front side of the chip 12 is transferred to the external surface of the package 10 through the molding compound 28, the PCB 16, and the heat spreader 30, and heat that reaches the external surface of the package 10 is dissipated to the surrounding environment by convection and radiation. FIG. 3 shows the results of a computer simulation of heat dissipation from the device of FIGS. 1 and 2 and shows a temperature gradient distribution. As shown in FIG. 3, since the molding compound and the PCB have the low thermal conductivity, the heat generated in the chip may not be effectively dissipated. This ineffective heat dissipation raises the junction temperature in the chip, and can cause a decrease in the data processing speed, erroneous operation, and electrical failure of semiconductor devices.